Problem: $\dfrac{7}{10} + \dfrac{15}{100} = {?}$
Answer: The fractions must have the same denominator before you can add them. Rewrite $\dfrac{7}{10}$ as $\dfrac{70}{100}$ $\dfrac{70}{100} + \dfrac{15}{100} = {?}$ $ = \dfrac{85}{100}$